It is extremely important for your tarantula to always have water within its reach. They seldom drink, but when they do, they drink a lot. Remember that your tarantula can move thanks to it locomotive hydraulic system, and it is obviously very important for all its biological processes.
The dreadful customary sponge
How can we give it water? Never do it with a cotton ball or the dreadful sponge, as previously recommended for a long time. To drink, the tarantula needs to submerge the front part of its prosoma. Between its chelicerae, it has its tiny mouth that it will use to suck the water. Therefore, it must always have a wide-rim container with water to facilitate drinking. The only thing a cotton ball or a sponge will do is collect bacteria!
It is a good idea to have a deep bowl. This way evaporation will be slower than with shallow bowls imitating rocks that are usually sold, and you will save a lot of time by not having to fill the water bowl constantly.
An ideal bowl next to a less adequate one
The bowl’s rim should be level to the substrate, and never above it. For tree-dwellers, it would be good if you could attach the bowl at the middle part of the tank, since tarantulas usually drink water from higher elevations, specially water that collects inside plants, such as bromeliads and orchids, and they never climb down to the ground to drink. But if you can’t do this, don´t worry, place it at ground level, and she will find it with no trouble, because your tank can’t be that big that the spider won’t find her way to the water fountain.
Tarantulas are extremely picky about their water. If it is dirty, they will never drink. Remember that their mouth is very small and they can’t afford to choke on a little piece of debris! So you must always be careful to keep the water bowl clean and replenished. Maybe the walls of the water bowl will be part of its new home, so I recommend that you just leave that bowl there, and place a new one with water someplace else.
A good idea to help crickets from drowning if they fall into the water bowl is to place a small rock they can cling to inside the bowl.
Lastly, another tip: Place two bowls, one inside the other. This way, when you need to change the water, you can leave the bottom one inside the substrate to maintain its space, and only remove the top one to clean or refill. This is shown in this video.